Many standard cancer chemotherapeutic agents act primarily through their ability to induce DNA damage causing tumor growth inhibition. However, these agents cause cell cycle arrest by induction of checkpoints at either S-phase or G2-M boundary. The G2 arrest allows the cell time to repair the damaged DNA before entering mitosis. CHK1 and an unrelated serine/threonine kinase, CHK2, play a central role in arresting the cell cycle at the G2-M boundary (O'Connell et al EMBO J (1997) vol 16 p 545-554). CHK1/2 induce this checkpoint by phosphorylating serine 216 of the CDC25 phosphatase, inhibiting the removal of two inactivating phosphates on cyclin dependent kinases (CDKs) (Zheng et al Nature (1998) vol 395 p 507-510). Another overlapping pathway mediated by p53 also elicits cycle arrest in response to DNA-damage. However, p53 is mutationally inactivated in many cancers, resulting in a partial deficiency in their ability to initiate a DNA-repair response. If CHK1 activity is also inhibited in p53-negative cancers, all ability to arrest and repair DNA in response to DNA-damage is removed resulting in mitotic catastrophe and enhancing the effect of the DNA damaging agents (Konarias et al Oncogene (2001) vol 20 p 7453-7463, Bunch and Eastman Clin. Can. Res. (1996) vol 2 p 791-797, Tenzer and Pruschy Curr. Med Chem (2003) vol 3 p 35-46). In contrast, normal cells would be relatively unaffected due to retention of a competent p53-mediated cell-cycle arrest pathway. The inhibition of DNA damage checkpoints is therefore expected to sensitise aberrantly proliferating cells to DNA damaging agents. Such sensitization is in turn expected to increase the therapeutic index of such chemotherapeutic agents or ionizing radiation. (Clary, D.O. Inhibition of Chk kinases in a leukemia model abrogates DNA damage checkpoints and promotes mitotic catastrophe. Proc Am Assoc Cancer Res (AACR) 2007, 48: Abst 5385) Therefore it is expected that efficacious inhibitors of CHK1 will lead to a corresponding Improvement in the efficacy of current DNA-damage inducing chemotherapeutic regimens (Sausville et al, J. Clinical Oncology (2001) vol 19 p 2319-2333). A number of putative CHK1 inhibitors are currently in phase I clinical trials including XL-844 (a dual CHK1/CHK2 inhibitor for the treatment of lymphoma and solid tumours), PF 00477736 (Phase I Study of PF-00477736 with gemcitabine in patients with advanced solid malignancies) & AZD7762 (Phase I open label multi center dose escalation study to assess safety tolerability and pharmacokinetics of AZD7762 administered as a single intravenous agent and in combo with weekly standard dose gemcitabine in patients with advanced solid malignancies). Thus, there remains an unmet medical need for low molecular weight CHK1 inhibitors with pharmacokinetic and pharmacodynamic properties making them suitable for use as pharmaceutical agents. The object of the present invention is to provide such pharmaceutical agents and treatments.
It has now been found that certain indolyl-pyridone derivatives show efficacy as CHK1 inhibitors.